conference paper emts 2013

8/10/2019 conference paper emts 2013

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SRR-loaded Antipodal Vivaldi Antenna for UWB

Applications with Tunable Notch FunctionDebdeep Sarkar

#1, Kumar Vaibhav Srivastava

#2,Member, IEEE

#Department of Electrical Engineering, Indian Institute of Technology, Kanpur

1 [email protected]@iitk.ac.in

Abstract This paper presents design of a novel compact

UWB antipodal Vivaldi antenna, where band-notch

characteristics within 5-6 GHz frequency range is achieved by

placing a parasitic rectangular SRR near the radiating arm, in

order to reduce electromagnetic interference with IEEE 802.11a

and HIPERLAN/2 systems. Simulation results show that the

proposed antenna provides wide impedance band-width with

satisfactory rejection in the desired band along with good gain

and stable radiation pattern in the rest of the UWB regime.

I.

INTRODUCTIONDesign of Ultra-Wideband (UWB) antennas for

state-of-the-art wireless communication has drawn

the attention of researchers since FCC first

approved the rules for the commercial utilization of

the unlicensed 3.1-10.6 GHz frequency band [1].

Various UWB antenna topologies have been

proposed in order to overcome the challenges of

achieving good impedance matching and radiation

stability within compact size and low

manufacturing cost [2-3]. Among them, antipodal

Vivaldi antennas (AVA) are attractive choice due totheir broad impedance bandwidth, symmetric end-

fire beam and ease of implementation in planar

PCB technology [4-6].

Electromagnetic Interference (EMI) due to the

existing narrowband communication systems like

WiMAX, WLAN (IEEE 802.11a, HIPERLAN-2)

and X-band systems is one of the major concerns

for UWB antenna engineers. Instead of using

additional band-stop filters (which would increase

antenna-footprint) for providing the desired notch-

band, the approach of embedding different-shaped

slots (C-shaped, H-shaped) in the radiator or ground

plane of the antenna, acting as intrinsic filters, have

become very popular in the antenna community [7-

8]. Meta-resonators like complementary split-ringresonators (CSRRs) have also found application in

design of UWB antennas with multiple notch-bands

[9].

This paper proposes a novel compact AVA

where the notch-band in the 5-6 GHz band is

achieved by properly placing a single rectangular

split-ring resonator (SRR) in vicinity of the

radiating arm of the antenna. The SRR acts as a

sub-wavelength resonator (size: /10-by-/12 with

respect to the notch frequency) and produces the

desired band-rejection in the IEEE 802.11a and

HIPERLAN/2 WLAN frequencies along with stable

far-field radiation pattern in the radiating band.

The paper is organised as follows. In section-II,

design of the reference AVA is presented. In

section-III, the comparison of the proposed and

reference AVA are shown, which is followed by

concluding discussions in section-IV.

II. DESIGN OF REFERENCE UWB AVA

The geometry of the reference balanced antipodal

Vivaldi antenna is shown in Fig.1. The tapered

radiation structure is designed from the intersection

of two quarter-ellipses according to the principle

followed in [5].

Fig. 1. Geometry of the balanced antipodal Vivaldi antenna which usesdesign principle in [5] (unit: mm)

Copyright 2013 IEICE

Proceedings of the "2013 International Symposium on Electromagnetic Theory"

23AM1F-03

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Metallization is provided symmetrically on both

sides of the 1.6 mm thick FR-4 epoxy substrate

(dielectric constant = 4.4, loss tangent tan = 0.02)

as is evident from Fig. 1. FEM-based commercial

electromagnetic simulator HFSS is used for

simulation of the antenna. It is found fromsimulation-results that the antenna provides good

impedance bandwidth matching (VSWR < 2) over

the UWB frequency range (3.1-10.6 GHz) along

with good far-field gain.

III.DESIGN OF SINGLE BAND-NOTCHED UWB AVA:RESULTSAND COMPARISON

A.Dimensions and Positioning of Parasitic Split-Ring

Resonator

The frequency response of a rectangular split ring

resonator (SRR) placed in microstriplineenvironment is studied by principle adopted in [10]

for different structural parameters (length and width

of split-rings, ring-spacing, split-gap dimensions).

To provide the desired notch-band, the rectangular

SRR is placed near one radiating arm of the

reference AVA as a parasitic element. The

dimensions of the SRR (as shown in Fig. 2) are

chosen such that its fundamental resonance

frequency lies in the middle of WLAN frequency

band (5.15-5.85 GHz).

Next the SRR position is varied to find outwhere the best band-notch characteristics in the

desired frequency range is achieved without

disturbing the impedance matching in other

frequency bands. Fig. 3 shows VSWR plots of the

antenna for the positions of the SRR with respect to

the AVA. It is observed that for position-1, the band

rejection is not at all satisfactory. For position-3,

although we get band-rejection in desired WLAN

range, impedance-matching deteriorates for higher

frequency. Hence for the proposed SRR-loaded

AVA, position-2 is chosen as optimum (Fig. 4).

Fig. 2. Dimensions of the rectangular SRR used as parasitic element (unit:

mm)

Fig. 3. Plot of VSWR of the band-notched antenna with respect to the

frequency for three different positions of the SRR

B.Performance of single SRR-loaded AVA

The variation of VSWR with frequency for the

proposed AVA as well as the reference antenna as

shown in Fig. 1 is illustrated in Fig. 5. It is observed

that the proposed antenna has impedance band-

width (3.1-11.4 GHz) covering the entire UWBspectrum along with the notch band in the

frequency range (5.15-6.07 GHz) which

encompasses the upper-WiMAX/WLAN band. The

maximum band-notch is achieved at 5.55 GHz

(VSWR=6.399).

Fig. 6 shows the comparison of peak realized far-

field gain of the proposed and reference antenna in

the range 3-11 GHz. It is seen that the gain-plot of

the proposed antenna closely follows that of the

reference UWB antenna, except the desired notch

band where a strong dip is observed.

Fig. 4. Proposed band-notched AVA with optimized SRR dimension and

position (unit: mm)

Fig. 5. VSWR versus frequency plots of the proposed antenna and the

reference antenna


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Fig. 7 shows the vector-plot of the surface

current distribution on the radiating arms of the

antenna as well as the SRR at three frequencies, the

middle one being the notch frequency at 5.55 GHz

to give an insight into the radiation-mechanism and

the band-rejection principle of the proposed AVA.

Strong surface-current density on the SRR, whichacts as a high Q-resonator at the notch frequency

5.55 GHz, compared to that on the radiating arms

suggest the reason for non-radiating behaviour of

the proposed AVA in the desired notch band.

Fig. 6. Peak-gain (dBi) versus frequency plots of the proposed antenna and

the reference antenna

Fig. 8 and Fig. 9 respectively show the 3D-gainplots of the reference and proposed band-notched

AVA at 4 GHz (below the notch frequency) and 8

GHz (above the notch frequency). It is evident that

the far-field radiation pattern is not seriouslyaffected due to the presence of the parasitic SRR.

C.Performance of identical antenna-pairs in far-field

To validate that the proposed antenna

successfully blocks out the desired notch band, we

perform the simulation of a transceiver antenna

system, keeping the two identical antennas in far-field (distance between antennas = 90 mm). Fig. 10

shows the simulated magnitude (dB) and phase (in

degrees) of the S21for the two-antenna system. The

magnitude of the transmission coefficient S21 (dB)

shows a dip in the desired region. The variation of

phase of S21 with frequency also implies the

presence of notch-band.

Fig. 7. Surface Current Distributions on the antenna conductors and SRR

at three different frequencies

Fig. 8. 3D-gain plots of the reference AVA at 4 GHz (top) and 8 GHz

(bottom) respectively


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Fig. 8. 3D-gain plots of the proposed AVA at 4 GHz (top) and 8 GHz (bottom)respectively

Fig. 10. Magnitude (dB) and phase (in degree) of S21for two identical band-

notched AVA placed in far-field region

IV.CONCLUSION

An SRR-loaded antipodal Vivaldi antenna having

UWB characteristics with notch band in the 5-6

GHz frequency range has been designed. The

impedance bandwidth and far-field behavior of the

proposed antenna has been investigated by HFSS

simulations.The proposed antenna is low-profile and uses

low-cost FR-4 substrate. To validate the simulation

results, the antenna would be fabricated and tested

in near future. Since the band-rejection property is

achieved via the rectangular SRR element placed

near the radiating arm of the antenna, it can be

tuned by changing SRR dimensions and positions.

Hence, multiple band-notched antennas for UWB

applications can be designed using the principle

used in this paper.

ACKNOWLEDGMENT

The authors would like to acknowledge all the

members of the Microwave circuit and Microwave

Metamaterials Laboratory (Department of Electrical

Engineering, IIT Kanpur) for their inspiration and

IIT Kanpur authority for the financial assistance.

REFERENCES

[1] Federal Communications Commission Revision of Part 15 of the

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[3] Y. J. Ren and K. Chang, An Annular Ring Antenna for UWBCommunications, vol. 5, no. 1, pp. 274-276, 2006.

[4] E. Gazit, Improved design of the Vivaldi antenna, IEE Proceedings

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